Imaging lens and imaging apparatus

ABSTRACT

An imaging lens consists of a first lens-group consisting of a positive lens with its surface that has the smaller absolute value of a curvature-radius facing an object-side, a positive lens in meniscus-shape with its convex-surface facing the object-side, a positive lens with its surface that has the smaller absolute value of a curvature-radius facing the object-side, and a negative lens with its surface that has the smaller absolute value of a curvature-radius facing an image-side, an aperture stop, a second lens-group consisting of a negative lens with its surface that has the smaller absolute value of a curvature-radius facing the object-side, a positive lens with its surface that has the smaller absolute value of a curvature-radius facing the image-side, and a positive lens, and a third lens-group consisting of a positive lens and a negative lens in this order from the object-side. A predetermined conditional expression is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2013/004895 filed on Aug. 19, 2013, which claims priority under 35U.S.C. §119(a) to Japanese Patent Application No. 2012-188196 filed onAug. 29, 2012. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens and an imagingapparatus. In particular, the present invention relates to an imaginglens used in electronic cameras, such as a digital camera, a camera forbroadcasting, a camera for surveillance and a camera for film making,and an imaging apparatus including the imaging lens.

2. Description of the Related Art

As an imaging lens used in an imaging apparatus, such as a video cameraand an electronic still camera, which uses an imaging device, such as aCCD (Charge Couple Device) and a CMOS (Complementary Metal OxideSemiconductor), as a recording medium, imaging lenses, for example, asdisclosed in Japanese Unexamined Patent Publication No. 2009-251399(Patent Document 1) and Japanese Unexamined Patent Publication No.2011-253050 (Patent Document 2) have been proposed.

SUMMARY OF THE INVENTION

As the definition of digital cameras and cameras for film making becamehigh in recent years, imaging lenses in which various aberrations areexcellently corrected have become needed. Further, a demand for imaginglenses having small F-number FNo., which are so-called fast imaginglenses, has been increasing. Further, when the imaging lens is used asan interchangeable lens, the imaging lens needs to have at least ashortest necessary length of back focus, and an incident angle of raysentering an image sensor in a peripheral area of an angle of view needsto be small to some extent.

In the imaging lens disclosed in Patent Document 1, various aberrationsare excellently corrected, and an incident angle of rays entering animage sensor in a peripheral area of an angle of view is relativelysmall. However, a back focus is insufficient. Further, the total lengthof the imaging lens is long relative to the focal length of the imaginglens.

In the imaging lens disclosed in Patent Document 2, a total length isshort, but an incident angle of rays entering an image sensor in aperipheral area of an angle of view is large.

In view of the foregoing circumstances, it is an object of the presentinvention to provide an imaging lens having a small FNo., and in whichvarious aberrations are excellently corrected, and an incident angle ofrays entering an image sensor in a peripheral area of an angle of viewis small, and it is possible to secure a sufficient back focus, and alsoan imaging apparatus including this lens.

An imaging lens of the present invention consists of a first lens group,a stop, a second lens group that moves during focusing and has positiverefractive power, and a third lens group that is fixed during focusingand has positive refractive power in this order from an object side.Further, the first lens group consists of an 11th lens having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the object side, a 12th lens having positiverefractive power in meniscus shape with its convex surface facing theobject side, a 13th lens having positive refractive power with itssurface that has the smaller absolute value of a curvature radius facingthe object side, and a 14th lens having negative refractive power withits surface that has the smaller absolute value of a curvature radiusfacing an image side in this order from the object side. Further, thesecond lens group consists of a 21st lens having negative refractivepower with its surface that has the smaller absolute value of acurvature radius facing the object side, a 22nd lens having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the image side, and a 23rd lens havingpositive refractive power in this order from the object side. Further,the third lens group consists of a 31st lens having positive refractivepower and a 32nd lens having negative refractive power in this orderfrom the object side. Further, the following conditional expression issatisfied:−0.1<f/f1<0.2  (1), where

f: a focal length of an entire system, and

f1: a focal length of the first lens group.

In the imaging lens of the present invention, it is desirable that thefirst lens group moves during focusing.

Further, it is desirable that the first lens group and the second lensgroup integrally move during focusing.

Further, it is desirable that the following conditional expression issatisfied:−0.3<(R12A−R12B)/(R12A+R12B)<0  (2), where

R12A: a curvature radius of an object-side surface of the 12th lens, and

R12B: a curvature radius of an image-side surface of the 12th lens.

Further, it is desirable that the following conditional expression issatisfied:0.3<Ds/L12<0.6  (3), where

Ds: a sum of an air space immediately before the stop and an air spaceimmediately after the stop, and

L12: a distance between a surface closest to the object side in thefirst lens group and a surface closest to the image side in the secondlens group.

Further, it is desirable that the following conditional expression issatisfied:1.2<f/f2<1.7  (4), where

f: a focal length of an entire system, and

f2: a focal length of the second lens group.

Further, it is desirable that the following conditional expression issatisfied:0.1<f/f3<0.6  (5), where

f: a focal length of an entire system, and

f3: a focal length of the third lens group.

Further, it is desirable that the following conditional expression issatisfied:35<vd1p<55  (6), where

vd1p: an average Abbe number of all the positive lenses in the firstlens group.

Further, it is desirable that the following conditional expression issatisfied:−0.05<f/f1<0.15  (1-1).

Further, it is desirable that the following conditional expression issatisfied:−0.25<(R12A−R12B)/(R12A+R12B)<−0.05  (2-1).

Further, it is desirable that the following conditional expression issatisfied:0.3<Ds/L12<0.5  (3-1).

Further, it is desirable that the following conditional expression issatisfied:1.25<f/f2<1.5  (4-1).

Further, it is desirable that the following conditional expression issatisfied:0.2<f/f3<0.5  (5-1).

An imaging apparatus of the present invention includes theaforementioned imaging lens of the present invention.

An imaging lens of the present invention consists of a first lens group,a stop, a second lens group that moves during focusing and has positiverefractive power, and a third lens group that is fixed during focusingand has positive refractive power in this order from an object side.Further, the first lens group consists of an 11th lens having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the object side, a 12th lens having positiverefractive power in meniscus shape with its convex surface facing theobject side, a 13th lens having positive refractive power with itssurface that has the smaller absolute value of a curvature radius facingthe object side, and a 14th lens having negative refractive power withits surface that has the smaller absolute value of a curvature radiusfacing an image side in this order from the object side. Further, thesecond lens group consists of a 21st lens having negative refractivepower with its surface that has the smaller absolute value of acurvature radius facing the object side, a 22nd lens having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the image side, and a 23rd lens havingpositive refractive power in this order from the object side. Further,the third lens group consists of a 31st lens having positive refractivepower and a 32nd lens having negative refractive power in this orderfrom the object side. Further, the following conditional expression issatisfied. Therefore, it is possible to provide an imaging lens having asmall FNo., and in which various aberrations are excellently corrected,and an incident angle of rays entering an image sensor in a peripheralarea of an angle of view is small, and it is possible to secure asufficient back focus.−0.1<f/f1<0.2  (1)

Further, the imaging apparatus of the present invention includes theimaging lens of the present invention. Therefore, bright video imageswith high image qualities are obtainable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section illustrating the lens configuration of animaging lens according to an embodiment of the present invention (alsoExample 1);

FIG. 2 is a cross section illustrating the lens configuration of animaging lens in Example 2 of the present invention;

FIG. 3 is a cross section illustrating the lens configuration of animaging lens in Example 3 of the present invention;

FIG. 4 is a cross section illustrating the lens configuration of animaging lens in Example 4 of the present invention;

FIG. 5, Sections A through E are aberration diagrams of the imaging lensin Example 1 of the present invention;

FIG. 6, Sections A through E are aberration diagrams of the imaging lensin Example 2 of the present invention;

FIG. 7, Sections A through E are aberration diagrams of the imaging lensin Example 3 of the present invention;

FIG. 8, Sections A through E are aberration diagrams of the imaging lensin Example 4 of the present invention; and

FIG. 9 is a schematic diagram illustrating the configuration of animaging apparatus according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiments of the present invention will be described in detailwith reference to drawings. FIG. 1 is a cross section illustrating thelens configuration of an imaging lens according to an embodiment of thepresent invention (also Example 1). An example of configurationillustrated in FIG. 1 is also the configuration of an imaging lens inExample 1, which will be described later. In FIG. 1, the left side is anobject side, and the right side is an image side.

This imaging lens consists of first lens group G1, aperture stop St,second lens group G2 that moves during focusing and has positiverefractive power, and third lens group G3 that is fixed during focusingand has positive refractive power, along optical axis Z, in this orderfrom an object side. Here, aperture stop St illustrated in FIG. 1 doesnot necessarily represent the size nor the shape of the aperture stop,but a position on optical axis Z.

When this imaging lens is applied to an imaging apparatus, it isdesirable to arrange a cover glass, a prism, and various filters, suchas an infrared ray cut filter and a low-pass filter, between an opticalsystem and image plane Sim based on the structure of a camera on whichthe lens is mounted. Therefore, FIG. 1 illustrates an example in whichparallel-flat-plate-shaped optical members PP1, PP2, PP3, which areassumed to be such members, are arranged between third lens group G3 andimage plane Sim.

First lens group G1 consists of 11 th lens L11 having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the object side, 12th lens L12 having positiverefractive power in meniscus shape with its convex surface facing theobject side, 13th lens L13 having positive refractive power with itssurface that has the smaller absolute value of a curvature radius facingthe object side, and 14th lens L14 having negative refractive power withits surface that has the smaller absolute value of a curvature radiusfacing an image side in this order from the object side.

Further, second lens group G2 consists of 21st lens L21 having negativerefractive power with its surface that has the smaller absolute value ofa curvature radius facing the object side, 22nd lens L22 having positiverefractive power with its surface that has the smaller absolute value ofa curvature radius facing the image side, and 23rd lens L23 havingpositive refractive power in this order from the object side.

Further, third lens group G3 consists of 31st lens L31 having positiverefractive power and 32nd lens L32 having negative refractive power inthis order from the object side.

Further, the imaging lens is configured in such a manner that thefollowing conditional expression (1) is satisfied.−0.1<f/f1<0.2  (1), where

f: a focal length of an entire system, and

f1: a focal length of the first lens group.

In the imaging lens of the present invention, a so-called modifiedGauss-type lens is configured by first lens group G1, aperture stop St,and second lens group G2 that has positive refractive power. When thislens is compared with a typical Gauss-type lens consisting of sixlenses, more excellent correction of a spherical aberration is possibleby changing two positive lenses arranged toward the object side ofaperture stop St to three positive lenses. When 12th lens L12, which hasbeen added in this case, has meniscus shape with its convex surfacefacing the object side, it is possible to reduce FNo. while suppressinggeneration of a spherical aberration and a coma aberration.

Further, when third lens group G3, which is fixed during focusing andhas positive refractive power, is arranged toward the image side ofsecond lens group G2, it is possible to suppress a fluctuation ofcurvature of field during focusing.

Further, when the lower limit of conditional expression (1) issatisfied, that is advantageous to reducing the total length. When theupper limit of conditional expression (1) is satisfied, that isadvantageous to maintaining a back focus. Further, it is possible togive appropriate positive refractive power to second lens group G2 andthird lens group G3, and to keep an incident angle of rays entering animage sensor in a peripheral area of an angle of view small.

Here, when the imaging lens satisfies the following conditionalexpression (1-1), more excellent characteristics are obtainable.−0.05<f/f1<0.15  (1-1).

In the imaging lens of the present invention, it is desirable that firstlens group G1 moves during focusing. When this mode is adopted, it ispossible to excellently correct various aberrations through the entirefocus range.

Further, it is desirable that first lens group G1 and second lens groupG2 integrally move during focusing. When this mode is adopted, it ispossible to simplify the structure of a focus mechanism.

Further, it is desirable that the following conditional expression (2)is satisfied. When conditional expression (2) is satisfied, it ispossible to reduce FNo. while keeping generation of a sphericalaberration and a coma aberration at a low level. When a certain degreeof refractive power is given to 12th lens L12, if the value is lowerthan the lower limit of conditional expression (2), or if the valueexceeds the upper limit of conditional expression (2), a sphericalaberration due to under-correction tends to be generated. Therefore,when this conditional expression (2) is satisfied, a burden on otherlenses as to correction of these aberrations is reduced. Here, when theimaging lens satisfies the following conditional expression (2-1), moreexcellent characteristics are obtainable.−0.3<(R12A−R12B)/(R12A+R12B)<0  (2); and−0.25<(R12A−R12B)/(R12A+R12B)<−0.05  (2-1), where

R12A: a curvature radius of an object-side surface of the 12th lens, and

R12B: a curvature radius of an image-side surface of the 12th lens.

Further, it is desirable that the following conditional expression (3)is satisfied. When the lower limit of conditional expression (3) issatisfied, that is effective in correcting astigmatism. When the upperlimit of conditional expression (3) is satisfied, that is advantageousto reducing a total length. Here, when the imaging lens satisfies thefollowing conditional expression (3-1), more excellent characteristicsare obtainable.0.3<Ds/L12<0.6  (3); and0.3<Ds/L12<0.5  (3-1), where

Ds: a sum of an air space immediately before the stop and an air spaceimmediately after the stop, and

L12: a distance between a surface closest to the object side in thefirst lens group and a surface closest to the image side in the secondlens group.

Further, it is desirable that the following conditional expression (4)is satisfied. When the lower limit of conditional expression (4) issatisfied, it is possible to keep an incident angle of rays entering animage sensor in a peripheral area of an angle of view small withoutmaking the refractive power of third lens group G3 too strong. When theupper limit of conditional expression (4) is satisfied, it is possibleto keep a spherical aberration in an excellent state. Here, when theimaging lens satisfies the following conditional expression (4-1), moreexcellent characteristics are obtainable.1.2<f/f2<1.7  (4); and1.25<f/f2<1.5  (4-1), where

f: a focal length of an entire system, and

f2: a focal length of the second lens group.

Further, it is desirable that the following conditional expression (5)is satisfied. When the lower limit of conditional expression (5) issatisfied, it is possible to keep an incident angle of rays entering animage sensor in a peripheral area of an angle of view small. Further, itis possible to suppress a fluctuation of curvature of field due tofocusing. When the upper limit of conditional expression (5) issatisfied, it is possible to make combined refractive power of firstlens group G1 and second lens group G2 strong. Therefore, a movementamount during focusing is suppressed, and it becomes possible to reducethe size of the system. Further, it is possible to reduce time requiredfor focusing. Here, when the imaging lens satisfies the followingconditional expression (5-1), more excellent characteristics areobtainable.0.1<f/f3<0.6  (5); and0.2<f/f3<0.5  (5-1), where

f: a focal length of an entire system, and

f3: a focal length of the third lens group.

Further, it is desirable that the following conditional expression (6)is satisfied. When the lower limit of conditional expression (6) issatisfied, that is effective in correcting a longitudinal chromaticaberration. When the upper limit of conditional expression (6) issatisfied, that is effective in correcting secondary chromaticaberrations.35<vd1p<55  (6), where

vd1p: an average Abbe number of all the positive lenses in the firstlens group.

In the imaging lens of the present invention, it is desirable to useglass as a specific material arranged most toward the object side.Alternatively, transparent ceramic may be used.

When the imaging lens of the present invention is used in toughenvironments, it is desirable that a multilayer coating for protectionis applied. Further, an anti-reflection coating for reducing ghost lightor the like during usage may be applied besides the coating forprotection.

FIG. 1 illustrates an example in which optical members PP1, PP2, PP3 arearranged between the lens system and image plane Sim. Instead ofarranging various filters, such as a low-pass filter and a filter thatcuts a specific wavelength band, between the lens system and image planeSim, the various filters may be arranged between lenses. Alternatively,a coating having a similar action to that of the various filters may beapplied to a lens surface of one of the lenses.

Next, numerical value examples of the imaging lens of the presentinvention will be described. Numerical values in the following tables 1through 9 and aberration diagrams illustrated in FIGS. 5 through 8 arenormalized so that the focal length of the entire system when the lenssystem is focused on an object at infinity is 100.

First, an imaging lens in Example 1 will be described. FIG. 1 is a crosssection illustrating the lens configuration of the imaging lens inExample 1. Optical members PP1, PP2, PP3 are also illustrated in FIG. 1and FIGS. 2 through 4 corresponding to Examples 2 through 4, which willbe described later. Further, the left side is the object side, and theright side is the image side. Illustrated aperture stop St does notnecessarily represent the size nor the shape of aperture stop, but aposition on optical axis Z.

The imaging lens in Example 1 consists of first lens group G1, aperturestop St, second lens group G2 that moves during focusing and haspositive refractive power, and third lens group G3 that is fixed duringfocusing and has positive refractive power, along optical axis Z, inthis order from an object side.

First lens group G1 consists of 11 th lens L11 having positiverefractive power in meniscus shape with its convex surface facing theobject side, 12th lens L12 having positive refractive power in meniscusshape with its convex surface facing the object side, 13th lens L13having positive refractive power in meniscus shape with its convexsurface facing the object side, and 14th lens L14 having negativerefractive power in meniscus shape with its concave surface facing animage side in this order from the object side. Here, 13th lens L13 and14th lens L14 are cemented together.

Second lens group G2 consists of 21st lens L21 in biconcave shape withits surface that has the smaller absolute value of a curvature radiusfacing the object side, 22nd lens L22 in biconvex shape with its surfacethat has the smaller absolute value of a curvature radius facing theimage side, and 23rd lens L23 in biconvex shape with its surface thathas the smaller absolute value of a curvature radius facing the imageside in this order from the object side. Here, 21st lens L21 and 22ndlens L22 are cemented together.

The third lens group G3 consists of 31st lens L31 in biconvex shape withits surface that has the smaller absolute value of a curvature radiusfacing the image side and 32nd lens L32 having negative refractive powerin meniscus shape with its concave surface facing the object side inthis order from the object side. Here, 31st lens L31 and 32nd lens L32are cemented together.

When 11th lens L11 has a meniscus shape with its convex surface facingthe object side, it is possible to suppress generation of astigmatism.When 12th lens L12 and 13th lens L13 have meniscus shapes, each of whichhas its convex surface facing the object side, it is possible tosuppress generation of a spherical aberration, a coma aberration andastigmatism. When 14th lens L14 has a meniscus shape with its concavesurface facing an image side, it is possible to reduce a difference inspherical aberrations according to wavelengths.

When 21st lens L21 has its surface that has the smaller absolute valueof a curvature radius facing the object side, this surface and animage-side surface of 14th lens L14 are symmetric with aperture stop Sttherebetween. Therefore, it is possible to cancel out coma aberrations.When 22nd lens L22 has its surface that has the smaller absolute valueof a curvature radius facing the image side, this surface and anobject-side surface of 13th lens L13 are symmetric with aperture stop Sttherebetween. Therefore, it is possible to cancel out coma aberrations.Further, it is possible to suppress generation of astigmatism. When 23rdlens L23 has its surface that has the smaller absolute value of acurvature radius facing the image side, it is possible to suppressgeneration of astigmatism.

When 31st lens L31 has its surface that has the smaller absolute valueof a curvature radius facing the image side, it is possible to suppressgeneration of astigmatism. When 32nd lens L32 has its surface that hasthe smaller absolute value of a curvature radius facing the object side,it is possible to suppress generation of astigmatism.

Table 1 shows basic lens data of the imaging lens in Example 1, andTable 2 shows data about specification of the imaging lens in Example 1.Next, the meanings of signs in the tables will be described by usingExample 1 as an example. The meanings of signs in Examples 2 through 4are basically similar to Example 1.

In the lens data of Table 1, a column of Si shows the surface number ofi-th surface (i=1, 2, 3 . . . ) that sequentially increases toward theimage side when a most object-side surface of composition elements isthe first surface. A column of Ri shows the curvature radius of the i-thsurface, and a column of Di shows a surface distance on optical axis Zbetween an i-th surface and an (i+1)th surface. Further, a column of Ndjshows a refractive index for d-line (wavelength is 587.6 nm) of a j-thoptical element (j=1, 2, 3 . . . ) that sequentially increases towardthe image side when a most object-side optical element is the firstsurface. Similarly, a column of vdj shows an Abbe number of the j-thoptical element for d-line (wavelength is 587.6 nm).

Here, the sign of a curvature radius is positive when a surface shape isconvex toward the object side, and negative when a surface shape isconvex toward the image side. The basic lens data show also aperturestop St and optical member PP. In the column of surface numbers, theterm “(STOP)” is written together with the surface number of a surfacecorresponding to aperture stop St.

Data about specification in Table 2 show focal length f′, back focusBF′, F-number Fno., and full angle 2ω of view.

In the basic lens data and the data about specification, degrees areused as the unit of angles. However, no unit is present for the othervalues because the values are normalized.

TABLE 1 EXAMPLE 1•LENS DATA Ndj νdj Si Ri Di (REFRAC- (ABBE (SURFACE(CURVATURE (SURFACE TIVE NUM- NUMBER) RADIUS) DISTANCE) INDEX) BER)  180.32644 8.595 1.74400 44.78  2 671.19394 0.133  3 56.55478 11.1991.80610 33.27  4 90.66373 6.739  5 144.99505 6.342 1.49700 81.54  6655.54098 1.843 1.84661 23.78  7 31.22907 19.600  8(STOP) ∞ 10.320  9−27.21338 1.941 1.51742 52.43 10 319.36441 12.741 1.61800 63.33 11−37.41115 0.135 12 235.29912 5.172 1.71299 53.87 13 −94.97119 5.942 14216.03099 10.662 1.49700 81.54 15 −86.45397 3.989 1.58144 40.75 16−411.54561 4.937 17 ∞ 3.000 1.58832 41.28 18 ∞ 41.066 19 ∞ 1.333 1.5168064.20 20 ∞ 0.267 21 ∞ 1.733 1.51680 64.20 22 ∞ 7.736

TABLE 2 EXAMPLE 1•SPECIFICATION (d-LINE) f′ 100.00 Bf′ 57.92 FNo. 1.912ω[°] 24.8

FIG. 5, Sections A through E are aberration diagrams of the imaging lensin Example 1. FIG. 5, Sections A through E illustrate a sphericalaberration, sine condition, astigmatism, distortion and a lateralchromatic aberration, respectively.

The aberration diagrams of a spherical aberration, sine condition,astigmatism and distortion illustrate aberrations when d-line(wavelength is 587.6 nm) is a reference wavelength. The aberrationdiagram of the spherical aberration illustrates aberrations for d-line(wavelength is 587.6 nm), C-line (wavelength is 656.3 nm), F-line(wavelength is 486.1 nm) and g-line (wavelength is 435.8 nm) by a solidline, a long broken line, a short broken line and a dotted line,respectively. The aberration diagram of the astigmatism illustratesaberrations for a sagittal direction and a tangential direction by asolid line and a broken line, respectively. The aberration diagram ofthe lateral chromatic aberration illustrates aberrations for C-line(wavelength is 656.3 nm), F-line (wavelength is 486.1 nm) and g-line(wavelength is 435.8 nm) by a long broken line, a short broken line anda dotted line, respectively. In the aberration diagram of the sphericalaberration and the aberration diagram of sine condition, Fno. means anF-number. In the other diagrams, ω represents a half angle of view.

Next, an imaging lens in Example 2 will be described. FIG. 2 is a crosssection illustrating the lens configuration of the imaging lens inExample 2.

The imaging lens in Example 2 is similar to the imaging lens in Example1 except that 13th lens L13 and 14th lens L14 are not cemented together,and that a cemented surface of 21st lens L21 and 22nd lens L22 is aconcave surface facing the object side. The absolute value of thecurvature radius of the cemented surface of 21st lens L21 and 22nd lensL22 is large in a similar manner to Example 1. Therefore, there is nogreat difference in the effects.

Table 3 shows basic lens data of the imaging lens in Example 2, andTable 4 shows data about specification of the imaging lens in Example 2.Further, FIG. 6, Sections A through E are aberration diagrams of theimaging lens in Example 2.

TABLE 3 EXAMPLE 2•LENS DATA Ndj νdj Si Ri Di (REFRAC- (ABBE (SURFACE(CURVATURE (SURFACE TIVE NUM- NUMBER) RADIUS) DISTANCE) INDEX) BER)  1106.14408 10.900 1.77250 49.60  2 1296.19109 8.489  3 48.35243 9.9981.80518 25.42  4 56.95540 0.267  5 56.77243 7.040 1.61800 63.33  693.37192 3.349  7 163.36512 2.526 1.84666 23.78  8 30.94222 20.581 9(STOP) ∞ 13.670 10 −26.13455 2.098 1.62004 36.26 11 −231.89447 9.6561.61800 63.33 12 −32.00752 0.267 13 230.31263 5.674 1.83400 37.16 14−97.65407 1.980 15 196.10293 9.977 1.49700 81.54 16 −120.41841 2.2341.80610 33.27 17 −318.64193 2.009 18 ∞ 2.009 1.90682 21.20 19 ∞ 4.017 20∞ 3.080 1.51680 64.20 21 ∞ 48.916

TABLE 4 EXAMPLE 2•SPECIFICATION (d-LINE) f′ 100.00 Bf′ 58.03 FNo. 1.902ω[°] 24.8

Next, an imaging lens in Example 3 will be described. FIG. 3 is a crosssection illustrating the lens configuration of the imaging lens inExample 3.

The imaging lens in Example 3 has a similar shape to the imaging lens inExample 2.

Table 5 shows basic lens data of the imaging lens in Example 3, andTable 6 shows data about specification of the imaging lens in Example 3.Further, FIG. 7, Sections A through E are aberration diagrams of theimaging lens in Example 3.

TABLE 5 EXAMPLE 3•LENS DATA Ndj νdj Si Ri Di (REFRAC- (ABBE (SURFACE(CURVATURE (SURFACE TIVE NUM- NUMBER) RADIUS) DISTANCE) INDEX) BER)  1100.63712 14.331 1.70154 41.24  2 2014.52281 0.133  3 53.93510 11.3851.71299 53.87  4 68.84798 2.906  5 54.93004 9.353 1.80610 33.27  664.00342 1.854  7 124.15715 3.332 1.84666 23.78  8 29.33479 23.493 9(STOP) ∞ 12.556 10 −27.90285 2.013 1.58144 40.75 11 −2720.71456 11.6051.71299 53.87 12 −37.01591 0.132 13 255.17819 4.433 1.74400 44.78 14−109.02860 14.799 15 162.91070 11.555 1.49700 81.54 16 −90.89983 2.6671.84666 23.78 17 −186.79591 37.332 18 ∞ 1.333 1.51680 64.20 19 ∞ 0.26720 ∞ 1.733 1.51680 64.20 21 ∞ 7.759

TABLE 6 EXAMPLE 3•SPECIFICATION (d-LINE) f′ 100.00 Bf′ 47.38 FNo. 1.902ω[°] 24.8

Next, an imaging lens in Example 4 will be described. FIG. 4 is a crosssection illustrating the lens configuration of the imaging lens inExample 4.

The imaging lens in Example 4 is similar to the imaging lens in Example1 except that the cemented surface of 13th lens L13 and 14th lens L14 isa concave surface facing the object side. The absolute value of thecurvature radius of the cemented surface of 13th lens L13 and 14th lensL14 is large in a similar manner to Example 1. Therefore, there is nogreat difference in the effects.

Table 7 shows basic lens data of the imaging lens in Example 4, andTable 8 shows data about specification of the imaging lens in Example 4.Further, FIG. 8, Sections A through E are aberration diagrams of theimaging lens in Example 4.

TABLE 7 EXAMPLE 4•LENS DATA Ndj νdj Si Ri Di (REFRAC- (ABBE (SURFACE(CURVATURE (SURFACE TIVE NUM- NUMBER) RADIUS) DISTANCE) INDEX) BER)  181.50514 8.543 1.80610 33.27  2 612.45693 7.471  3 53.44536 10.2551.83400 37.16  4 71.74002 1.510  5 114.64171 8.593 1.53715 74.81  6−487.45056 3.333 1.84666 23.78  7 30.52797 18.693  8(STOP) ∞ 10.168  9−27.39761 1.613 1.51742 52.43 10 158.78094 12.547 1.61800 63.33 11−39.10354 0.133 12 548.33896 5.111 1.71299 53.87 13 −74.49228 15.190 14124.10376 11.750 1.49700 81.54 15 −106.99366 4.000 1.54814 45.79 16−2419.83302 40.818 17 ∞ 1.333 1.51680 64.20 18 ∞ 0.267 19 ∞ 1.7331.51680 64.20 20 ∞ 7.789

TABLE 8 EXAMPLE 4•SPECIFICATION (d-LINE) f′ 100.00 Bf′ 50.90 FNo. 1.902ω[°] 24.8

Table 9 shows values corresponding to conditional expressions (1)through (6) about the imaging lenses in Examples 1 through 4. In all ofthe examples, d-line is a reference wavelength. The following Table 9shows values at this reference wavelength.

TABLE 9 EXPRESSION NUMBER CONDITIONAL EXPRESSION EXAMPLE 1 EXAMPLE 2EXAMPLE 3 EXAMPLE 4 (1) f/f1 0.02 0.09 0.05 −0.04 (2) (R12A −R12B)/(R12A + R12B) −0.23 −0.08 −0.12 −0.15 (3) Ds/L12 0.35 0.36 0.370.33 (4) f/f2 1.29 1.31 1.29 1.27 (5) f/f3 0.27 0.25 0.37 0.38 (6) νd1p53.20 46.12 42.79 48.41

As the data show, all the imaging lenses in Examples 1 through 4 satisfyconditional expressions (1) through (6). It is recognizable that theimaging lenses are fast lenses, and that various aberrations areexcellently corrected in the imaging lenses.

Next, an imaging apparatus according to an embodiment of the presentinvention will be described. FIG. 9 is a schematic diagram illustratingthe configuration of an imaging apparatus using an imaging lensaccording to an embodiment of the present invention, as an example of animaging apparatus according to an embodiment of the present invention.In FIG. 9, each lens group is schematically illustrated. This imagingapparatus is, for example, a video camera, an electronic still camera orthe like using a solid-state imaging device, such as a CCD and a CMOS,as a recording medium.

An imaging apparatus 10, such as a video camera, illustrated in FIG. 9includes an imaging lens 1, a filter 6, an imaging device 7 and a signalprocessing circuit 8. The filter 6 is arranged toward the image side ofthe imaging lens 1, and has a function as a low-pass filter or the like,and the imaging device 7 is arranged toward the image side of the filter6. The imaging device 7 converts an optical image formed by the imaginglens 1 into electrical signals. For example, a CCD (Charge CoupledDevice), a CMOS (Complementary Metal Oxide Semiconductor) and the likemay be used as the imaging device 7. The imaging device 7 is arranged insuch a manner that an imaging surface of the imaging device 7 and theimage plane of the imaging lens 1 match with each other.

An image imaged by the imaging lens 1 is formed on an imaging surface ofthe imaging device 7. Signals about the image are output from theimaging device 7, and operation processing is performed on the outputsignals at the signal processing circuit 8. Further, an image isdisplayed on a display device 9.

So far, the present invention has been described by using embodimentsand examples. However, the present invention is not limited to theembodiments nor to the examples, and various modifications are possible.For example, values of a curvature radius, a surface distance, arefractive index, an Abbe number and the like of each lens element arenot limited to the values in the numerical value examples, but may beother values.

What is claimed is:
 1. An imaging lens consisting of: a first lensgroup; a stop; a second lens group that moves during focusing and haspositive refractive power; and a third lens group that is fixed duringfocusing and has positive refractive power in this order from an objectside, wherein the first lens group consists of an 11th lens havingpositive refractive power with its surface that has the smaller absolutevalue of a curvature radius facing the object side, a 12th lens havingpositive refractive power in meniscus shape with its convex surfacefacing the object side, a 13th lens having positive refractive powerwith its surface that has the smaller absolute value of a curvatureradius facing the object side, and a 14th lens having negativerefractive power with its surface that has the smaller absolute value ofa curvature radius facing an image side in this order from the objectside, and wherein the second lens group consists of a 21st lens havingnegative refractive power with its surface that has the smaller absolutevalue of a curvature radius facing the object side, a 22nd lens havingpositive refractive power with its surface that has the smaller absolutevalue of a curvature radius facing the image side, and a 23rd lenshaving positive refractive power in this order from the object side, andwherein the third lens group consists of a 31st lens having positiverefractive power and a 32nd lens having negative refractive power inthis order from the object side, and wherein the following conditionalexpression is satisfied:−0.1<f/f1<0.2  (1), where f: a focal length of an entire system, and f1:a focal length of the first lens group.
 2. The imaging lens, as definedin claim 1, wherein the first lens group moves during focusing.
 3. Theimaging lens, as defined in claim 1, wherein the first lens group andthe second lens group integrally move during focusing.
 4. The imaginglens, as defined in claim 1, wherein the following conditionalexpression is satisfied:−0.3<(R12A−R12B)/(R12A+R12B)<0  (2), where R12A: a curvature radius ofan object-side surface of the 12th lens, and R12B: a curvature radius ofan image-side surface of the 12th lens.
 5. The imaging lens, as definedin claim 1, wherein the following conditional expression is satisfied:0.3<Ds/L12<0.6  (3), where Ds: a sum of an air space immediately beforethe stop and an air space immediately after the stop, and L12: adistance between a surface closest to the object side in the first lensgroup and a surface closest to the image side in the second lens group.6. The imaging lens, as defined in claim 1, wherein the followingconditional expression is satisfied:1.2<f/f2<1.7  (4), where f: a focal length of an entire system, and f2:a focal length of the second lens group.
 7. The imaging lens, as definedin claim 1, wherein the following conditional expression is satisfied:0.1<f/f3<0.6  (5), where f: a focal length of an entire system, and f3:a focal length of the third lens group.
 8. The imaging lens, as definedin claim 1, wherein the following conditional expression is satisfied:35<vd1p<55  (6), where vd1p: an average Abbe number of all the positivelenses in the first lens group.
 9. The imaging lens, as defined in claim1, wherein the following conditional expression is satisfied:−0.05<f/f1<0.15  (1-1), where f: a focal length of an entire system, andf1: a focal length of the first lens group.
 10. The imaging lens, asdefined in claim 1, wherein the following conditional expression issatisfied:−0.25<(R12A−R12B)/(R12A+R12B)<−0.05  (2-1), where R12A: a curvatureradius of an object-side surface of the 12th lens, and R12B: a curvatureradius of an image-side surface of the 12th lens.
 11. The imaging lens,as defined in claim 1, wherein the following conditional expression issatisfied:0.3<Ds/L12<0.5  (3-1), where Ds: a sum of an air space immediatelybefore the stop and an air space immediately after the stop, and L12: adistance between a surface closest to the object side in the first lensgroup and a surface closest to the image side in the second lens group.12. The imaging lens, as defined in claim 1, wherein the followingconditional expression is satisfied:1.25<f/f2<1.5  (4-1), where f: a focal length of an entire system, andf2: a focal length of the second lens group.
 13. The imaging lens, asdefined in claim 1, wherein the following conditional expression issatisfied:0.2<f/f3<0.5  (5-1), where f: a focal length of an entire system, andf3: a focal length of the third lens group.
 14. An imaging apparatuscomprising: the imaging lens, as defined in claim 1.